drivers: pinctrl: wch_20x_30x_afio: fix afio remap

- Enable AFIO clock prior to remap configuration
- Consolidate remap logic in a single conditional block
- Correct USART1 remap detection by checking pcfr_id
- Apply changes to pinctrl_wch_afio.c

Signed-off-by: Jianxiong Gu <jianxiong.gu@outlook.com>